The key to hatching BBS is to have a heat source. Use a heater (If using a huge amount or if it will be over night).Or get a heating bulb, or even a lamp that just sits above the container with the BBS. Also make sure that you keep aeration throughout the tank by having an air stone in the container.
In a day and some hours, you should definitely have some BBS!
This is a nice and easy way to SEE how to hatch BBS, if you're a more visual person:
Good Luck and Let us know how everything goes!